Signaling



Sept. 27, 1949. JOHNSON ET AL; 2,482,914

SIGNALING Filed June 27, 1945 INVENTUM. HA ,QW/UKJOH/VSOM Patented Sept. 27, v1949 4'UNITED STATES PATENT OFFICE l.

SIGNALING Harwiek Johnson and Vernon D. Landon, Princeton, N. J., and Alpha M. Wiggins, South Bend, Ind., assignors to Radio Corporation of America, a corporation of Delaware Application June 27, 1945, Serial No. 601,'198v 5 claims. 1

The present application discloses a new and improved means for modulating the frequency or timing or oscillatory energy. In the particular arrangement. used for disclosing our invention, the. oscillations are of ultra high frequency, corresponding to a wavelength of the order of centimeters, and the modulation is in accordance with modulation currents of triangular wave form. It will be understood that the invention is applicable to oscillations of lower frequency and to modulation currents of any type such as, for example, voice or code signals.

An object of our invention is provision of an improved means for modulating the timing orr frequency of high frequency oscillatory energy.

In frequency modulation systems operating at ultra high frequencies, considerable care must be taken in arranging'the modulator and relating the same to the generator circuits. This is because the reactance or impedance of the modulator must be kept small, since otherwise it interferes with the operation of the ultra high frequency oscillator.

An object of our invention is to provide an improved modulator for ultra high frequency generators the reactance of which is small and mostly variable, `so that the same does not unduly influence the maximum frequency at which the generator being modulated may work.

In the present invention, the above objects are attained by provision of an improved variable capacity to be includedvin the ultra high frequency circuit. One capacity element isy attached to and varied in position by a diaphragm driven by a modulation current winding in the eld between the pole pieces of the magnetic structure. The variable capacity element or condenser plate is associated with a fixed condenser plate, and both are included in the high frequency circuit of an oscillator for .modulation purposes.

improved diaphragm and voice coil arrangement such that the capacity changes are proportional to modulation current intensity, thereby providing a straight line relationship between the frequency of the generated oscillations and the time of recurrence of the characteristics on vthe modulation current. This object is attained by a diaphragm and voice coil arrangement such that there is no breaking up of the diaphragm at `the higher frequencies. Moreover, in order to keep the diaphragm stiffness about the same at all temperatures, the diaphragm is clamped be tween members of similar material so that contraction and expansion of both members 'is the Same.

During operation-of modulators as disclosed here, it is often necessary to change or adjust slightly-the center frequency of the system, i.: e., the unmodulated carrier frequency. In the modulator of our invention the movable condenser plate is in the form of a cylinder carried by the The modulator embodiment we are describing is used in a radio ranging system. oscillations are generated, radiated, and reected back from some distant object. Inorder to determine the distance to the object, thegenerated oscillations are modulated as to frequency by currents having characteristics which recur sequentially at equal time intervals and are detected and counted to measure the distance to the object. In this embodiment, a straight line relation between the frequency of the ultra high frequency oscillations and the timing of the recurring characteristics on the modulation current is desired.

An object of our invention is to provide diaphragm and overlapping the fixed plate in the form of a disc (end of th e inner cable of a line) coaxial with the fixed plate. A Vernier condenser plate is arranged vcoaxially with respect to the two main plates and is adjustable in position with respect to the fixed plate of the condenser.

The magnetic modulator of the present invention is, as stated above, to bev used in ultra high frequency circuits. When so used, we have found that the ultra high frequency oscillatory energy is radiated through the gap in the pole pieces and lost as useful output.

An object of our present invention is to provide a modulator of this type including means for preventing this loss of radiation energy. This object is accomplished by shunting and/or closing the gap between the pole pieces by means oi a non-magnetic conductive material such as a copper ring which shields the magnetic structure from the radio currents to prevent radiation and loss thereof.

The modulator of the present invention and the oscillator controlled thereby are to be used by the armed forces under battle conditions, and, obviously, to be useful for this purpose the modulator and the associated apparatus must be structurally strong and reliable in operation under adverse conditions.

A further object of our invention is the provision of a modulator in the form of a variable capacity which is structurally strong, very reliable an in operation under adverse conditions, and of a simple nature, so that it may be operated by relatively inexperienced personnel.

In describing our invention in detail, referenc will be made to the attached drawings, wherein Figs. l, 2 and 3 illustrate by end view, by side view, and by a sectional view, respectively, a condenser modulator and oscillator modulated thereby, arranged'in accordance with our invention. Fig. 4 illustrates by simplified wiring diagram the oscillator and modulator of Fig. 3, while Fig. 5 is a basic diagram of the modulator of Fig. 3 and its electrical relation to the oscillator tube and chassis.

The variable condenser comprises two plates 2 and 4 of which plate 2 is the movable plate, and in the embodiment illustrated is cylindrical in form. Plate 4 is fixed-and mounted coaxially with respect to plate 2. There is clearance between the cylindrical member 2 and the xed plate 4 so that on the application of modulation currents to winding 8, plate 2 moves up and down to vary the capacity between plate 2 and plate 4. The condenser also includes a Vernier plate 6 adjustably mounted on the axis of the cylindrical condenser plate 2 and the fixed plate 4. This vernier plate 6 permits small adjustments of the mean or carrier or non-modulated frequency of the oscillations developed or appearing in any circuit coupled with the modulator. Such a circuit might then be as illustrated in Fig. 4, wherein thevariable condenser formed by plates 2 and 4 is between the anode and grid of a grounded grid oscillator, the cathode of which is operating at high radio frequency potential. The plate 4 in this embodiment is then connected to the anode of the tube and the modulator structure or case is connected to the grid and to ground.

The magneticvstructure designated generally at 5 may be of the Alnico V type and may take various forms. In the embodiment shown, Figs. 2 and 3, the inner pole piece 5 is somewhat circular in form (of varying diameter) and the outer pole pieces 5" may be elliptical in contour as shown by the dotted lines in Fig. 1. The magnet, however, is so arranged that the modulation winding 8 carried by the diaphragm D is located between thepole pieces and properly spaced with respect thereto. The diaphragm carries. as stated above, the cylindrical condenser plate 2 and the modulation winding 8. The magnetic structure 5. 5 and 5" is permanently attached (forced fit, welded. or bolted etc.) to a base member I8 in the form of an annular ring having shoulders, and a depression for purposes described hereinafter. A ring member 20 is bolted by machine screws 2| to the member Ill. The diaphragm D is retained between the members I0 and 2l). The inner periphery of the ring member 28 is threaded and a tension ring 24 is threaded into member 20 against the diaphragm. The tension ring 24 has its inner end surface curved to fit into the depression of the base member I0. The diaphragm D, the clamping members I 0 and 20, ring 24 and a clamping member 28, may. as stated above, all be of Phosphor bronze or other similar material having like coefficients of expansion, and preferably small coefcients of expansion, so that the tension on the diaphragm will not change materially with changes in temperature. This keeps the stiness of the diaphragm the same at all temperatures. By turning the tension ring 24 into the threaded part of the outer clamping ring 20 to force the diaphragm D into the depression in the inner ring l0, increased tension is introduced in the diaphragm so that it becomes stiffer. By meansI of this tension the natural frequency ofv the diaphragm is controlled within small limits. The variations in stiffness in diaphragms resulting from variations in manufacturing arecontrolled by this ring 24.

The diaphragm D and modulation coil 8 are, in the embodiment illustrated, so arranged that there will be no breaking up of the diaphragm at the higher modulation frequencies. This is accomplished by centering the mass of the voice coil and keeping the distributed mass, i. e., the mass of the remainder of the diaphragm and voice coil support distributed and the compliance thereof small. In other words, the diaphragm has but one degree of freedom so that it responds linearly to the modulation current intensities.

A clamping ring 28 within the inner periphery of tension ring 24 is bolted to the inner clamping member I8 by bolts 29 which pass through, holes in the diaphragm. The clamping surface of the ring member 28 is beveled slightly to be raised at the inner periphery of the ring so that the diaphragm D is gripped tightly between members I0 and 28 after the proper tension has been applied by tension ring 24. The bevel is exaggerated considerably in the drawings in the sake of clearness.

An insulator and spacer in the form of an annular ring 38 is fastened to the clamping 28 by bolts 34. The fixed condenser plate 4 is on a shaft which extends through the member 30 and is retained therein properly spaced from the movable,

plate 2. The xed plate 4 may be integral with or fastened to a conductor which extends from the modulator and to which the connection from the high frequency circuit may be made. This electrode and connection are represented by condenser plate 4 and the lead therefrom to the anode of the tube in Fig. 4. The variable plates 2 and 6 are represented by grounded condenser plates 2 and 8 in Fig. 4. In the embodiment illustrated, condenser plate 4 is at the end of the inner cable of a coaxial line the outer cable of which is grounded. The shaft on which plate 4 is mounted is threaded as is a nut-like member 36, so that when the latter is tightened up the plate 4 is retained xed in member 38 properly spaced from plate 2. As will be described later, the anode electrode of a tube of the light-house type is electrically and mechanically connected by the annular member 36 to the condenser plate 4.

A closure member 50 slides over a shoulder on the inner clamping ring I0 and is retained in place by means of bolts 52 threaded into the end piece of the magnetic structure. A sleeve 56 the upper end of which is split to make good contact is forced into the magnetic structure coaxial with the inner pole piece 5. The Vernier condenser plate 6 is mounted on a shaft threaded into the inner pole piece 5 and extending through the sleeve 56. The end of the shaft for the vernier condenser plate extends out of casing 58 and is slotted so that the plate 8 may be adjusted towards and from the plate 4. The end of the closure member 50 has a thickened portion therein which is threaded to receive a cap 60 placed in position to close the structure after the proper adjustments are made. By adjustment of the position of the disc-like condenser plate 6 with respect to the plate 4, the static capacitance of the modulator is changed to change the mean frequency of a circuit tuned thereby. When the plate 4 is at the end of a transmission line as it is in the embodiment illustrated, adjustment of the position of plate 6 changes the static capacnance at the end of the une, thus altering the electrical length of the line and consequently the center frequency of the oscillator tuned by the said line.

One end of the modulation winding 8 is grounded, as is one side of the source of modulating potentials. The other side of the modulating potential source is connected by a lead to contact 63. Thislead may extend through the casing 50 as desired', for example, through opening I therein.

As stated above, the modulator of the present invention may be used in any alternating current circuit, such as a relay circuit or an oscillation generator for modulation purposes. In the embodiment being described, the condenser is used as the modulator of an ultra high frequency generating circuit. This circuit is as shown diagrammatically in Fig. 4. The condenser is indicated by numerals 2 and 4 and the distributed and/or lumped inductance at 9. The grid oi.' the tube is grounded as is the movable plate 2, while the fixed plate 4 is connected to the anode of the tube. This includes the modulator in the high frequency circuit, and we have found that radiation of ultra high frequency energy takes place in the magnetic structure through the gap between the pole pieces 5 and 5" wherein the modulation coil B is accommodated. The grounding effect of the modulator structure is therefore imperfect and permits leakage of the radio frequency energy. To prevent this leakage we im' prove and/or supplement the shielding provided by the magnetic structure. To prevent this radiation from taking place we weld or otherwise fix to the pole pieces'5' and 5" a non-magnetic metallic ring 68 which closes th gap to shield the modulator structure with respect to the high frequency currents and reduce the loss thereof. The ring 68 eiectively provides a continuous shield for the radio frequency but does not interfere with the magnetic circuit of the modulator.

The xed condenser plate 4, in the embodiment illustrated, is the end of the inner conductor of a coaxial cable forming the. anode line of an oscillation generator. This conductor is held in place by an insulator andspacer in the form of a thick annular ring 3U. The outer cable 64 of the coaxial line is slipped over the ring 30 and the shoulder on the inner clamping ring 28. A con-4 nection in the form of a threaded member 36 is threaded over the shaft-like member, towhich the plate 4 is attached, and tightened up to maintain the inner line xed in position. This ymember and member 4 may be considered the inner line of a coaxial cable. The member 36 may be slotted and drilled to receive the anode electrode 66 o'f a tube such as, for example, one of the lighthouse type. This line including 36, between the plate 4 and anode of the tube with the outer line 64 forms the tuned transmission line and is the timed anode circuit of the oscillator. The modulated oscillator then is basically as illustrated in Fig. 5. The resonant anode line has an electrical length of about 7i/2 including the effect of the terminating capacities and is electrically as shown in Fig. 5. Then, variation ofthe position of the cylindrical condenser plate 2 varies the walls of the tube and, the grid extends radially within the ring across the tube structure. The cathode C is in.a cathode cavity formed by the tube walls and the cathode cavity is tunable by plugs P, not shown in Fig. 3, but shown schematically in Fig. 5. The condenser andtube arrangement is integral with an oscillator assembly which is electrically as illustrated in Fig. 5. A clamping ring 10 slips over the cover 50 of the modulatorv to rest on the shoulder thereon. The ring 10 is threaded on its inner periphery, as is the circular end 14 of the generator and modulator chassis. The chassis, a portion of which is shown at 14, completely incloses the generator circuit and tube. rI he line member 64 also is part of the chassis and conductively connected to themember 14. Spring contact members 16 are arranged between the modulator and metallic member 64. Spring contact members 18 and 80 separate the structure into a cathode to grid cavity and a plate to grid cavity for tuning purposes. This chassis is at ground or equivalent radio frequency potential, as is the magnetic eld producing structure, the cylindrical condenser plate 2, the vernier plate 6, the outer line 64 of the cable, etc.

The oscillation generator otherwise may be of any appropriate type. In the embodiment shown schematically in Figs. 3 and 5. the tube is of the lighthouse" type, with its grid connected in shunt to the line to form'a cathode cavity tunable by means of plugs P, and a plate to grid cavity. In this embodiment the fixed condenser plate, as stated above, forms the lend of the inner transmission line,'which is in the form of a`sleeve into which the anode of the lighthouse tube is pressed. This sleeve .36 may be slotted to make good contact between the lighthouse tube anode and thev line formed by the support of the fixed plate 4. The diaphragm driven condenser plate 2 overlaps the end of this line, which includes the anode of the lighthouse tube, and the variable or trimmer condenser is arranged thereabove, as shown.

What is claimed is:

1. In a signalling system, a magnet having pole pieces between which there is a gap, an alternating current path of low impedance in shunt to said gap, a diaphragm mounted adjacent the said pole pieces, a winding carried by said diaphragm and extending into said gap, a firstcondenser plate mounted for movement by said diaphragm, a second condenser plate mounted in coupled relation with said first condenser plate, high frequency electrical connections to said plates, a Vernier plate mounted for adjustment relative to said second plate, and modulating'means for controlling the current through said winding.

2. In a signalling system, a magnet having pole pieces between which there is a gap, a diaphragm mounted adjacent the said pole pieces, a winding carried by said diaphragm and extending between said pole pieces, 'a rst condenser plate mounted for movement by said diaphragm, a second condenser plate mounted in coupled relation with said irst condenser plate, high frequency electrical connections to said plate, a Vernier plate coaxial with respect to said first two plates, an electrical "connection between one of said rst two plates and said Vernier plate, means for controlling the current through said winding, and a.v

radio frequency path of low. impedance in shunt to said gap. l

3. In a signalling system, in combination, a diaphragm, means for moving said diaphragm in accordance with modulating currents, a rst condenser plate mounted for movement by said diaphragm, a second condenser plate mounted in coupled relation with said rst condenser plate, an electron discharge tube having a cathode and having an anode coupled by a line to said second condenser plate, said tube having a grid coupled to said rst condenser plate which is at ground or equivalent radio frequency potential, and a tuned circuit coupling the cathode of said tube to ground or equivalent radio frequency potential.

4. A variable capacity including, a permanent magnet having opposed pole pieces the adjacent faces of which are circular in contour, a diaphragm mounted adjacent the said pole pieces, a cylindrical winding carried by said diaphragm and extending between the poles of said magnet,

a iirst cylindrical condenser plate mounted for movement by said diaphragm, a lsecond condenser plate mounted coaxially with respect-to and in coupled relation with said cylindrical condenser plate, electrical connections to said plates, a Vernier plate coaxial with respect to said rst two plates, an electrical connection between one of said rst two plates and said Vernier plate, and means for controlling the current through said winding.

5, In a signalling system, in combination, a diaphragm, means controlled by signals for moving said diaphragm in accordance with said signals, a first condenser plate mounted on said diaphragm for movement therewith, a second condenser plate mounted in coupled relation with said rst condenser plate, an electron discharge tube having a cathode and having an anode 8 coupled by a line to said second condenser plate, said tube having a grid coupled to said first condenser plate which is at ground or equivalent radio frequency potential, and a tunable line coupling the cathode of said tube to ground.

' HARW'ICK JOHNSON. VERNON D. LANDON. ALPHA M. WIGGINS.

REFERENCES CITED The following references are of record in the le of this patent:

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